Pneumatic Circuits :
(Drawn by R.Ramakutty)
(Drawn by R.Ramakutty)
Sunday 18 March 2018
Wednesday 14 March 2018
Friday 9 March 2018
shuttle valve & fast exhaust valve
A shuttle valve, also known as a double check valve, allows pressure in a line to be obtained from alternative sources. It is primarily a pneumatic device and is rarely found in hydraulic circuits.
Construction is very simple and consists of a ball inside a cylinder, as shown in Figure 4.25a. If pressure is applied to port X, the ball is blown to the fight blocking port Y and linking ports X and A. Similarly, pressure to port Y alone connects ports Y and A and blocks port X. The symbol of a shuttle valve is given in Figure 4.25b.
A typical application is given in Figure 4.25c, where a spring return cylinder is operated from either of two manual stations. Isolation between the two stations is provided by the shuttle valve. Note a simple T-connection cannot be used as each valve has its A port vented to the exhaust port.
Two-Step Speed Control System From Fluid Power with Applications By Esposito
Clamping and bending
—Valve A above applies air to the up end of the clamp cylinder through shuttle valve B. The operator then actuates valve C to extend the bend cylinder and reset valve A. Shuttle valve B maintains pressure in the clamp cylinder. When the operator releases valve C, low-pressure air from reducing valve D retracts the clamp cylinder. The pilot line of valve A is vented, and the system is ready for the next operation.
A fast exhaust valve (
-Figure 4.26) is used to vent cylinders quickly. It is primarily used with spring return (single- acting) pneumatic cylinders. The device shown in Figure 4.26a consists of a movable disc which allows port A to be connected to pressure port P or large exhaust port R. It acts like, and has the same symbol as, a shuttle valve. A typical application is shown in Figure 4.26b.
Fast exhaust valves are usually mounted local to, or directly onto, cylinders and speed up response by avoiding any delay from return pipes and control valves. They also permit simpler control valves to be used.
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Introduction to Fluid Power
By James Johnson
Tuesday 6 March 2018
Coordinate Measuring Machine, Throttle Governing Of Steam Turbine:- similar to Pelton wheel governing
gify.com
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| Coordinate Measuring Machine http://www.mechanicaltutorial.com/different-types-of-governing-system-in-steam-turbine . Throttle Governing Of Steam Turbine:-
Throttle Governing of steam Turbine is most popular and easiest way to control the turbine speed. When steam turbine controls its output speed by varying the quantity of steam entering the turbine is called Throttle Governing. It is also known as Servomotor methods.
In this system, a centrifugal governor is driven from the main shaft of turbine by belt or gear arrangement. A control valve is used to control the direction of oil flow which supplied by the pipe AA or BB. The servomotor or relay valve has a piston which moves towards left or right depending upon the pressure of oil flow through the pipes AA or BB. This cylinder has connected a needle which moves inside the nozzle.When the turbine is running at normal speed, everything in the turbine such as such control valve, servomotor, piston position, fly balls of centrifugal governor will be in their normal position as shown in the figure. The mouth of both pipes AA or BB is closed into the control valves.
Assume that the turbine's load increases. It will decrease its speed which will decrease the centrifugal force of the turbine. Now fly balls of the governor will come down thus decreasing their amplitude. These fly balls also bring down the sleeve. The sleeve is connected to a control valve rod through a lever pivoted on the fulcrum. This down word sleeve will raise the control valve rod. Now oil is coming from the from the oil sump, pumped by gear pump is just stay at the mounts of both pipes AA or BB which are closed by the two wings of control valves. So, raise of control valve rod will open the mouth of the pipe AA but BB is still closed. Now the oil pressure is coming from the pipe AA. This will rush from the control valve which will move the right side of the piston. As a result, the steams flow rate into the turbine increases which will bring the speed of the turbine to the normal range. When speed of the turbine will come to its normal range, fly balls will come into its normal position. Now, sleeve and control valve rod will back to its normal position.
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